Installation of all packages under Unix

Dear List-Members,

does anyone know a simple way to automatically install all R packages  
on a unix system to the default library path? Not from inside R, it  
should rather work as a shell script - job at startup.

Something like R cmd install -l pkgs ### where pkgs should mean all  
packages (is there an option to control overwriting?)

Thanks a lot,

N. Boehme